Funds are requested from the division of Research Resources for the purchase of a VG ZAB-2VE high performance double focusing mass spectrometer. The instrument will have a mass range of 10,000 Daltons at an accelerating voltage of 8 kV. It will have continuously variable resolution up to 125,000 with a transmission of 2% at 20,000 resolution. It is proposed to equip the instrument with a focal plane electrooptical detector. This recent development in detector technology can be readily fitted and used without having to break the vacuum seal. It consists of a microchannel plate in combination with a linear photodiode array. The detector can operate at low resolution (1,000) where 15% of the mass range is covered and at high resolution (10,000) where 4 % of the mass range is covered. With this detector it will be possible to obtain instantaneous mass spectra. Recent demonstrations have shown that this provides an increase in sensitivity of up to two orders of magnitude compared with operation in the full scanning mode. It is also proposed that a Cs+ ion gun be fitted to the instrument so that high sensitivity liquid secondary ionization mass spectra of high molecular weight biomolecules can be obtained. This technique is 5-10 times more sensitive than fast atom (xenon) bombardment mass spectrometry. Thus, it will be possible to obtain an increase in sensitivity of at least three orders of magnitude when compared with the double focusing mass spectrometers currently available at Vanderbilt. The ZAB instrument is equipped with a DEC VAX supermicrocomputer and so it will be possible to realistically carry out foreground/background operation of the instrument without the inordinate delays that are experienced with DEC PDPbased systems that are currently in use in our laboratory. It should-be possible to process data rapidly so that highly efficient use of the instrument will be possible. Long term data storage can also be carried out with great efficiency on cartridge tapes. The major users of the instrument will come form the Molecular Toxicology Center at Vanderbilt. Projects that will be carried out mainly involve the structural characterization of proteins, oligonucleotides and modified oligonucleotides. A group of minor users will also benefit in having access to the instrument in projects that range from the analysis of oxygenated proteins to structural characterization of high molecular weight phospholipids. It is anticipated that, in the future, the instrument will be of benefit to a number of other investigators at Vanderbilt.